OF CONCHOLOGY 31 



of the generic and specific definition. 

 Adamson in his ' Natural History of 

 Senegal/ printed at Paris, in 1757, 

 says that the external character of the 

 spire, varies according to the plane 

 they turn upon, which, he observes, is 

 either horizontal, cylindrical, conic or 

 ovoid. At the same time, he admits 

 that there are a great many interme- 

 diate forms, which cannot properly be 

 defined. 



It is a remarkable circumstance, 

 that many of the young shells, have 

 not the same number of wreaths as 

 the adults ; from which circumstance 

 it would appear, that the part of the 

 animal nearest the apex, never in- 

 creases in size. The number of 

 wreaths cannot, at all times, be de- 

 pended upon. 



Whorl is one of the wreaths or 

 volutions of the shell. Plate 2nd, fig. 

 8th, L; and plate 3d, fig. 10th, L. 



Depressed Spire is when the spire 



